Multiple-beam electron gun



Dec. 6, 1955 R. E. BENWAY MULTIPLE-BEAM ELECTRON GUN Filed April 3G, 1953 3 Sheets-Sheet l INVENTOR.

Robe/0L i Benn/ay NEY Dec. 6, 1955 R. E. BENWAY 2,726,347

MULTIPLE-BEAM ELECTRON GUN Filed April 30, 1953 3 Sheets-Sheet 2 IN VE N TOR.

Dec. 6, 1955 R. E. Bx-:NWAY 2,726,347

MULTIPLE-BEAM ELECTRON GUN Filed April 30, 1953 3 Sheets-Sheet 3 United States Patent O 2,726,347 MULTIPLE-BEAM ELECTRoN GUN Robert E. Benway, Lancaster, Pa., assignor to Radio Corporation of America, azcorporation of Delaware Application April 30, 1953, Serial No. 352,095

11 claims. (cl. 313-10) This invention is directed to electron discharge devices of the cathode ray tube type and more specifically to cathode ray tubes used as viewing tubes for color television.

One type of cathode ray viewing tube for color television, disclosed in the copending application of Hannah C. Moodey, Serial Number 295,225, filed June 24, 1952, utilizes three electron'guns for forming three parallel electron beams arranged'symmetrically about the tube axis and directed at a target electrode within the tube envelope. A combined converging and focusing lens, formed by potential differences between three electrodes, is used to converge the three electron` beams to a common point on the target.

The target electrode consists principally of a masking electrode formed of a thin metal sheet having a large number of small apertures formed therethrough. The apertured masking electrode is mounted substantially normal to the tube axis and in the pathsof the electron beams. Conventional means are used to scan the three beams simultaneously over the apertured mask electrode in a rectangular raster. A glass target support plate is mounted close and parallel to the side of the masking electrode opposite to the electron guns. v

There is formed on the glass support plate groups of phosphor dots with each group consisting of three dots spaced 120 from a common point which in turn is aligned with one of the apertures through the masking electrode so that there is one group of phosphor dots aligned with each aperture of the masking electrode. The three phosphor dots of each group are formed respectively of phosphors luminescing in different colors as red, green, and blue.

Since the three parallel beams of the color tube are converged to a common point on the masking electrode, the electrons of each beam strike the masking electrode from substantially three diiferent directions. As the beams are scanned over the masking electrode surface, the electrons from the three beams will pass through the apertures of the masking electrode along paths which are respectively extensions of the directions from which the beams strike the masking electrode and will strike separate phosphor dots of each group. This arrangement results in the electrons then of each beam striking phosphor dots which luminesce with one color.

A tube of the type described above can be utilized with various types of color systems in which the color signals are either formed and transmitted simultaneously or in a sequential order and in which each signal may comprise an elemental signal or a frame signal. kThe signals are applied each independently to the three guns of the viewing tube so that the three electron beams are independently modulated to provide the color response at vthe correct time interval.

Tubes of the type described above do not haveoptimum picture brightness because the masking electrode at the target inherently collects a large percentage of each beam. lt is desirable in tubes of this type to increase the screen eiciency, which is the percentage of each electron beaml which strikes the phosphor spots of the target. An obvious way to increase screen eliiciency would be to open the holes in the masking aperture to permit the passage of a greater proportion of each electron beam. However, the size of the apertures in the masking electrode is obviously limited to prevent the overlapping of the beams upon striking the phosphor dots whereby color dilution of the picture would result. It is also desirable in tubes of this type, for circuit reasons, to collect as little current as feasible in the gun.

It is, therefore, an object of this invention to provide a color picture tube of increased picture brightness.

It is another object of this invention to provide a color picture tube of improved gun efliciency.

It is also an object of `this invention to increase the screen eiiciency of a color picture tube having a beam masking electrode at the target.

The invention is specifically related to a color picture or viewing tube having a masking electrode at the target whereby electrons approaching the target from one of several directions will strike phosphor portions of the target luminescing with a single color of light. To improve the picture brightness of tubes of this type, the electron beams within the deflecting lields of the scanning yoke are made with a minimum cross section limited by the desired resolution of the picture of the tube. By decreasing the beam diameter in the deflection plane, it is. possible to enlarge the apertures of the masking electrode at the target and thus to increase the picture brightness or screen efliciency of the tube. 'Ihis resultis accomplished by providing a substantial prefocusing lens in the path of each electron beam. The prefocusing lens also increases the gun efficiency for its rrespective beam whereby certain circuit problems are alleviated.

Figure 1 is a sectional View of portions of a color picture tube, in accordance withthe invention.

Figure 1A' is an enlarged sectional View of a portion of the gun structure of the tube of Figure 1.

Figure 2 is a sectional view along line 2 2 of Figure 1.

v Figures 3, 4 and 4A are schematic representations of portions of the picture tube of Figure l.

Figures 5 and 6 are diagrammatic showings of the beaml paths in the tube of Figure 1, and in accordance with thev invention.

'Figures l and 1A show a color television picture tube consisting of an evacuated envelope 10 having an enlarged bulb or shell portion 12 iixed to a tubular neck portion 14. The tubular neck 14 and the bulb portion 12 are axially aligned along a common axis 16. Mounted at one end of the neck portion is an electron gun meansl 18 for providing a plurality of electron beams along paths which yare symmetrically spaced from the axis 16. Mounted 'substantially normal to the axis 16 of the tube and within the opposite end of the bulb portion 12 is a is in turn fixed within the short tubular control electrodeV 30 coaXially mounted within the neck portion 14. The cathode electrodes 26 are closed at the end facing the target 20 and are coated with thermionic emitting material (not shown) for providing sources of electrons. i

The control electrode 30 s closed at the end facing theV target 20 by a plate member 32 having a plurality of Patented Dec. 6, 1955 aperturestherethrough, with one aperture aligned with each coated end of the cathode electrodes Y26. Closely spaced along the axis 16 from the grid plate 32 is a rst accelerating electrode plate 34 mounted in a parallel plane to that of plate 32. Accelerating plate 34 is .also apertured, with one aperture aligned with each of the apertures in plate 32.

Spaced along the axis 16 is a second accelerating electrode 38 consisting of a tubular memberclosed at both ends by apertured plates 40 and 42,. respectively. Again, each aperture in plates 40 and 42 is aligned with a correspending aperture in the other plate and with an aligned pair of apertures in plates 32 and 34 to provide a straight line path for the passage of electrons from the respective cathode electrodes 26 through the Yaccelerating electrode 38.

Mounted within the tubular accelerating electrode 38 is a beam masking diaphragm or plate member 44, also having a plurality of apertures with one aperture aligned with each straight line-paths from cathodes 26 through the tubular electrode 38. Spaced along the axis 16 and mounted coaxially thereto is a third accelerating electrode 46 consisting of a short tubular member enclosing the straight line paths from the cathodes 26 to the screen 20; a fourth accelerating electrode is formed as a conductive coating 48 on the inner surface of the tubular envelope portion 14 and also encloses all of the straight line paths from Vtheseveral cathode electrodes 26 .to the screen 20.

The operation of the electron gun 18 is that in which appropriatevoltages are applied to the several electrodes as indicated 'in Figure 1. These voltage values are in no way limiting 'but represent typical voltages which have been used to operate tubes of this type. Within each cathode electrode 26 is mounted a heater lament, which, during tubeV operation, raises the temperature of the cathode emissivematerial to a thermionic level. The electrons emitted from each. cathode pass through the 'alignedv apertures in plates 32 and 34. AThe contiguration of the electrostatic tield formed between plates 32 and 34, at operating potentials, causes the electrons from each cathode to form a beam having a minimum cross sectional area or crossover point 33 adjacent plate 34 and as schematically shown in Figure l. From each crossover point 33`the electrons pass respectively into the tubular electrode 38 as diverging beams. The fringe portions of each beam are masked off or collected by the corresponding apertures of plate 44. The apertures in plate42 are sufficiently large that the central portions of each beam, passing through the .respective aperture of plate 44,110 not strikethe edges of these apertures in plate42.

4`Due to the differences of potential between electrodes 38 and1`461there is formed an electron lens lield 50 therebetween and as schematically shown in Figure 1. One portion of the lens eld 50 extends through the .aperturesfin accelerating electrode plate42 to form separate {ie-lds b52; with oneV eld 52.in the path of each electron beam. The elds 52 have a curvature of a` degree that changes the electron beams from diverging beams toconverging beams. The converging action of fields '52 focuses each beam` tol a small. spot on' the maskingelectrode 22 of target 20. "Fields52 Vconstitute the main or principal focusingfield foreach electron beam, respectively.

Between the third accelerating electrode 46 and the accelerating electrode coating 48, there is also established an electron lens eld 574 having somewhatthe conguration schematically vrshown in Figure 1. All of the beams pass through the common field S4and the-nature of .the field is to provide convergence of each: beam toward the'eld axiswvhich is, cornmon=with..axs.16,05the tube. AField S4 is adjustedtoibring theseveralizbeams to a common point of convergence on the axisv16: and at .thetarget masking screen 22. The common-converging tield` 54 also .adds somewhat to theifocusing Vofxtthe "electrode 22""of'the target.

electrons in each beam to a minimum spot on the masking The operation ofthe gun"18, as described above is similar to that described in the above cited copending application of Hannah C. Moodey.

On the surface of the glass support plate 24 of target 20, there is formed a large number of phosphor dots 56 and as shown more specifically in the enlarged sketches of Figures 3 and 4. The phosphor dots 56 are arranged in groups vof three, with the dots in each group-,spaced 120 about a common center point 55. Each.dot in every group is formed of a dierent fiuorescing phosphor material and,.as indicated in Figures3 and 4, the phosphor materials will luminesce with red, green, or blue light respectively when struck by high energy electrons. Figure 3 shows specifically one group of phosphor dots 56 and arranged as described above. The center 55 of the group is aligned with one aperture 58 ofthe masking electrode 22 and the arrangement is such that each of the apertures 58 of electrode22 has a corresponding group of three differently iluorescing phosphor dots aligned therewith and in a similar manner.

As shown in Figure 3, the screen structure Ais such that the alignment of each separate phosphor dot with its respective aperture 58 is along a directional line `X, Y, or Z, which forms a small angle with the line determined by the center of each aperture Y58 and the center 55 of the respective group of phosphor dots. This provides a structure such that electrons passing through thev aperture S8 of Figure 3 along each one of the directional lines X,Y, or Z will strike only one of the phosphor dots. The arrangement is utilized in forming the target electrode as shown in more detail in Figure 4 in which three electron beams, corresponding to. those shown in Figure l, upon converging to a common point on the masking screen 22 will approach the screen each from a different direction X, Y, or Z, which makes a small angle of incidence tothe normal of the masking electrode 22. The electrons of each beam striking the common point or spot of convergence on masking electrode 22 will pass through whatever apertures `58 are covered by the beam spot. Furthermore, the electrons passing through these apertures 58 will continue. in the same direction, X, Y,. or Z of their approach to screen 22 and will strikelthe specific phosphor spot aligned with each aperture 53 in that direction. Thus, from Figure 4 it can be seen that all of the electrons from one beam passing through electrode 22 will only strike those phosphor' spots which uoresce with -the same color and the screen 22 will mask the electrons of cach beam from all of the other phosphor spots uorescing with theother colors.

Means are. provided for scanning the three beams of Figures 1, 3, and 4 over the surface of the target 20. The deflecting means are shown schematically as a yoke structure 60 mounted on the tubular envelope portion 14. The yoke 60 isv of a conventional design and operation and is constituted principally of two pairs of coils, with the coils of each pair connected in series with each otherto a source of saw tooth currents for pro-Y viding line Vandframe scansion of the electron beams over the surface of target 20. The operation ofthe tube described is also disclosed in greater detail in thefabove cited copending application of Hannah C. Moodey.

In tubes of the type described, it is desirable to obtain a maximum screen brightness. However, since the masking aperture plate 22 at the target absorbs a large percentage of the beam current,.the brightness of the picture obtained is not a maximum. Also, as set forth in the article by H. B. Law, page 466 of the RCA Rcview, Part'll, September 1951, vthe screeneliciency can be expressed as the product of a constant.K `and the where M is the beam diameter in lthe deflection plane and Sis the beam-to-axis spacing in the deflection plane.

.As shown in Figure l when each beam is deflected by the fields of yoke 60 the direction of the beams is changed from the axis of the tube to approach the target 22 from a different direction. Each beam may be considered as originating from a deflection plane P, which is substantially at the center of the coils of the yoke 60. This plane can be determined, as schematically shown in Figure l, by projecting each beam path backwards onto its respective undeflected beam path. The points where the projected paths of the several beams meet their undeflected paths respectively determine this plane of deflection. From the above relationship, expressed for the screen efficiency of a tube of the type described, it can be seen that the reduction of each beam diameter, M, within the deflection plane increases the screen efliciency. This is due to the fact that, an electron beam of smaller diameter in the deflection plane, will cover less area of each phosphor spot 56. This effect is shown more specifically in Figure 4A where M1 represents a beam of a given diameter. Fringe electrons from the edge of the beam M1 striking the edge of an aperture 58 will strike the edge of a corresponding phosphor dot 56. The paths of these fringe electrons are indicated bythe solid lines drawn through aperture 58 toI the edge ofthe spot 56. The solid lines' thus determine the spread of the beam M1 ink passing through aperture 58. Aperture 58, then, must be suliiciently small to prevent the fringe electrons from spreading beyond the spot 56 to` strike additional neighboring phosphor spots and thus cause color dilution in the picture. However, if the beam diameter is madev smaller such as that indicated by Mz, for example, the spread of the beam, is smaller as indicated by the dotted lines representing the beam paths of the fringe electrons. Beam M2 strikes a smaller surface area of the corresponding spot 56. Because of this, then, the aperture 58 may be opened until the fringe electrons of the beam M2 will strike the edge of spot 56. By opening the aperture 58, more of the beam` passes through the aperture to strike the phosphor spot 56 and thus produce a brighter fluorescence from spot 56. This procedure increases the screen efliciency as described.

In accordance with the invention, then, there is established between the crossover points 33 of each beam and the respective focusing lens 52, an additional prefocusing lens 62, with one of each lens 62 in the path of each of the electron beams. Focusing fields 62 are formed by mounting on the face of plate 34, facing, the targeta plurality of apertured cup-like structures 63, forming short tubular extensions of the apertures in plate 34. Cups 63 are mounted von plate 34 with the open end of each cup facing the target electrode 20, andA with the aperture in the bottom of each cup 63 coaxially positioned about a corresponding aperture in plate 34. The prefocusing lenses 62 are formed by. establishing an appropriate difference of potential between electrodes 34 and 38. The cup electrodes 63 form each lens field 62 into one having a sharp curvature` dipping into each cup 36 respectively. This is shown schematically in Figure l.

The effect of the prefocusing lens field 62 is shown schematically in Figures and 6. As shown in `Figure 5 the electron emission from cathode 26 passes in substantially straight lines from the cathode emitting surface through the first crossover point 33, through the masking aperture 44 to the main focusing lens S2, and then in substantially straight converging paths through the deflection plane` P to the target 2G. The lens system ofthis type is one in whichl the first crossover region 33 of the Vbeam isimaged on the target 20. Since the first crossover point 33 is that portion of each beam having a minimum cross sectional area, the size of the beam spot on the target is increase in length of the image distance and the decreaseY determined by the magnification of the lens system and, as is well-known in the art, is proportional to the. ratio of the image distance to the object distance. As shown in-Figure 5, the object distance is that distance fromthe first crossover point 33 to the main focusing lens 52 and the image distance is substantially that distance from the main focusing lens 52 to the screen 20.

Figure 6 illustrates the effect of placing a prefocusing lens 62 beween the first crossover point 33 andthe main focusing lens 52. The lens 62 decreases the divergence of the electron beam from the first crossover point 33. Furthermore, the beam width or beam diameter is made smaller by lens 62 between the prefocusing lens and screen 20 and particularly so in the deflection plane. This enables the use oflargerapertures 58 in the target masking electrode 22 and in this manner increases the screen efliciency and the brightness of the picture of the tube as pointed out above.

However, from Figure 6 it can also be seen that the effect of using the additional prefocusing lens 62 is the same as that of moving the main focusing lens 52 toward the first crossover point 33. Actually, the two lenses have the same optical effect as a single equivalent lens identi fied by the dotted line 66 positioned between the plane of the main focusing lens 52 and the location of the pre focusing lens 62. The position of Vthis resultant single lens can be determined by projecting the electron paths from the first crossover point along their diverging directions and byprojecting backward the electron paths from: their converging directions. The intersections of these projections determine the plane 66 of the resultant single lens. Theobject distance then of the newlens system is substantially the distance from the first crossover point 33 to the plane 66 of the resultant single lens, and the image distance is that'from this plane 66 to the screen- 20. The magnification is again proportional to the ratio of the image distance to the object distance which is larger than 'inf the :previous lens system of Figure 5, due to the in length of theobject distance. The increased magnifica# tion of the lens system results in the beam spot at the target Y The magnification depends on the 20 becoming larger. strength of the prefocusing lens field 62. It is therefore necessary todetermine an optimum relationship between the picture resolution desired and the screen efliciency or picture brightness. In tubes of the type described, the resolution of the picture has been chosen as that of 700 lines and the prefocusing lens 62 is adjusted to provide this resolution with a resultant decreaseof beam diameter in the deflection plane. The apertures 58 are constructed then with increased openings to accommodate the change in beam diameter and to provide a brighter picture thanV previously obtained.

The size chosen for the cup electrodes 63 is determined by the shape of the field which they are to produce. The diameter of the cups can not be too small as the electron beam would then tend to pass through the edges of the fields 62 and would introduce beam distortions. Furthermore, the diameter can not be too large as they wouldnot provide sufficient curvature of the field to give the desired focusing effect. Furthermore, the diameter of the cups is limited by the spacing of the apertures in plate 34. In a tube of the type described, the apertures in plate 34 were spaced at approximately 6.2 mrn. This permitted the use of cups 63 having a depth of 3 mm. and a diameter of approximately 6 mm. Also the cup depth determines the strength of the prefocusing field 63: the field becomes l stronger as. the depth of the cup is increased since the field curvature is increased. y v Figure 6 also discloses an additional advantage of using prefocusing-fields in accordance with the invention. The' shaded areas inl Figures 5 and 6 schematically indicate the amount of the electron beam which is lost by being co1- lected by the apertureof the masking electrode 44. For the same beam emission and as shown in Figure 6, the

zgvaegaan -7 use of the prefocu'sing' -1ens"62`,by :introducingconvergence in'the `beam,"'permits'rnore=-o the beam ltopassf-through thewaperturerof-tthe plate144. This results in' higher. gun eiciency-which is desirable for-circuit reasons. Y

lntthe'mannerzdescribedaboveand in accordance with the :i invention the :use -of v the =prefocusingl2lensesf 62 in creases both the screen efliciency'rand `the beam density whichiresultsin: each case Jin increasing the `picture brightness othetube. Thisthenpermits using `the maximum eiciencyaofithe.- color screenr unit and yet still retaining axhighi'degree of picture resolution. IAs described, the inventionisthat which afproper balance is obtained betweenathe efciencyuof the screen unit,1the-e"1ciencyof the gun, :and the .picturel'esolution While eertain--rspecic Vembodiments have -been illust-ra.ted1arld,` desctibed,r.it` will' bev understood thatV various changes and modications maybe made therein without departing from the spirit and scope of the invention.

=Whatis claimed is:

.i1.An:,electrondischargexdevice comprising, electron gun means for providing a plurality of beams along respective -paths in; a;common.generaldirection, a target electrodenlountedA transversely to said beam paths, said gun means `including electrode-structure Vfor providinga common electrostatic converging Alens in the paths of the electron: beams, electrode .means for providing a plurality of principal focusing lenses, one of said focusing lenses in the pathfor-` each electron beam, and electrode means for forming aplurality,-of'zprefocusing lenses one .in the path of each beam. v

`12. IAn-4 pelectron discharge l, device ucomprising electron gunmeansufor providing a; plurality of electron beams along respective paths spaced from a common axis, a target; electroderspaced from said electron gun means and mounted transversely to said beam paths and said common axis,-` said electron. gun `means including cathode-means and ai first and a second-electrodespaced along said axis between saidV cathode means and said target for providing a plurality of` converging lenses one in the path of each beam,` a third electrode. spaced alongsaid .axis between saidfsecond electrodeand said target for formingy a pluralityof principal lensesone in the part of each of said beams.

3. An `electron discharge device comprising electron gun means `forrproviding a plurality of electron -beams along respective paths1spaced from a common axis, a targetelectrode Aspaced from said electron gun means and mounted transversely to said beam paths and said common axis,saidfelectronfgun'means including cathode means and-arstzand a second electrode spaced along said axis v between Said cathodezmeans and said targetfor providing a plurality ofconverging lenses one in thepath of each beam, a third electrode spaced alongsaid axis between said second ,electrode and said target for forming aplurality ofi-principal lenses one in the pathof each of said beams,;.saidi first;.e1ectrode including a plurality of aperturedfcup; electrodes, andv means mounting one cup electrode-coaxiallyzon each beam path with the open end of eaclrcup` electrode .adjacent said second electrode.

`4.19m electron `.discharge `device `comprising 'electron gun `aneansror` providingla plurality -o electron beams alongrespective. pathslspacedV from a common axis, a targetrelecnodespacedfrom-said electron gunimeans and mountedtransversely tosaid beam paths and said common'waxisp said `electron gun means vincluding cathode means and a rst and a second electrode spaced along said axisbetween said cathode means and said target for providinga plurality of converging lenses one in the path of each beam, a third electrode spaced along said axis between saidrsecondelectrode and said target for formingea pluralityuofzzprincipallenses one in thev path "of eaclznot asaidfbeamssaidfirst electrode including' a" pluralityzcfz aperturediy cup; electrodes; and" means mounting one. cup electrodecoaxiallyA on each'beam path with the open end of; each cupI electrode-adjacent said V'second' elec- IVs trode, said second gun electrode'comprising a-tubular member mounted 4`coaxially` withvsaid common axis* and a plate memberclosing-each end of said tubular-member, said plate members eachhaving aplurality of apertures therethrough with one'aperture in eachV plate alignedwith each beam pathA for the passage of the respective beam.

5. An 'electron discharge device comprising electronv gun means for providing a-plurality of electron beams along respectivepaths spaced -from a common axis, a target electrode spaced from said electron gun means and'mounted transversely to said beamV paths and said commonaxis, said electron gun means including cathode means and'a rst and a second electrode spaced along'said axis-between said cathode means and said'ltarget for providing avplurality of converging lenses one `in the path of each beam, a third electrode spaced along said axis between said second electrode and said target for forming-a plurality of principal lenses `one in thepath of each` of said beams, said rst electrode including a plurality of apertured cup electrodes and means mounting one cup electrode coaxially'on each beam path with the open end of each cup electrode adjacent said secondV electrode, said second gun electrode comprisingy -a tubular member mounted coaxially with said common axisand a plate member closing, each end of said tubularmember, said plate members each having a plurality of apertures therethrough with one` aperture in `each place aligned with each beam path forA the passage of the respective beam, and amasking platemounted within and intermediate the ends'of said tubular member, saidV masking plate having a plurality of apertures therethrough with one aperture aligned `with :the centerof each beam path for masking the outer portions of each beam respectively.

6. An electron discharge device comprising electron gun means for providing aplurality of electron beamsalong respective paths spaced from a common axis, a target electrode'fspaced from'said electron gun means and mounted transversely to-said beam paths and said common^ axis, said electron gun means including'cathode means anda first and afsecond electrode spaced along said axis be` tween said cathode means and said target for providing a plurality of converging lenses one `in the path of each beam, a third electrode spaced along saidv axis `between saidsecond electrode and said target for forming a plurality of principal lenses one in the path of each of said beams, and a common dellecting means between. said gun means and-said target electrode for scanning said beams over said target.

7.*An electron discharge device comprising electron gun means for providing a pluralityof electron beams along respective paths spaced from a common axis, a target electrode spaced from said electron gun means and mounted transversely to said beam paths and said common axis, said electron gun means including cathode means and a rst and a second electrode-spaced along said axis between said cathode means and-said target forrproviding a plurality of converging lenses one in the path of ea'ch beam, a third electrode spaced along said axis Abetween said second electrode and said target for forming a plu" rality of principal lenses one inthe path of each of said beam,` saidrst electrode including a plurality of apertured cup electrodes and means mounting one cup electrode coaxially on each beam path 'with the open end 'of each-cup electrode adjacent saidl second electrode, said second gun electrode comprising a tubular member mounted Vcoaxiallylwith said common axis and a plate member closingr each end'of said tubular member, said plate `members each having a plurality of apertures therethrough with one aperture in each `plate aligned with each beam path for the passageofithe respective beam, and a common deecting means between said` gunmeans and said target electrcdefor scanning'said Vbeams over'said target. b

8; -An=electron"discharge device comprising, electron gunfmeansforproviding a plurality of electron.` beams along respectivel paths spaced from a common axis, a

target electrode spaced from said electron gun means and mounted transversely to said beam paths and said common axis, said electron gun means including cathode means and a rst and a second electrode spaced along said axis between said cathode means and said target for providing a plurality of converging lenses one in the path of each beam, a third electrode spaced along said axis between said second electrode and said target for forming a plurality of principal focusing lenses one in the path of each of said beams, said lrst electrode including a plu rality of tubular electrodes and an apertured plate, said plate having an aperture in the path of each of said beams, said tubular members mounted on said plate with one tubular member over each aperture and an open end adjacent said second electrode.

9. An electron discharge device comprising, electron gun means for providing a plurality of electron beams along respective paths spaced from a common axis, a target electrode spaced from said electron gun means and mounted transversely to said beam paths and said common axis, said electron gun means including cathode means and a lirst and a second electrode spaced along said axis between said cathode means and said target for providing a plurality of converging lenses one in the path of each beam, a third electrode spaced along said axis between said second electrode and said target for forming a plurality of principal focusing lenses one in the path of each of said beams, said first electrode including a plurality of tubular electrodes and a plate having an aperture therethrough aligned with each beam path, and means mounting one of said tubular electrodes coaxially on each beam path with one end enclosing an aperture through said plate and with the other end of each of said tubular electrodes adjacent said second electrode.

10. An electron discharge device comprising, electron gun means for providing a plurality of electron beams along respective paths spaced from a common axis, a target electrode spaced from said electron gun means and mounted transversely to said beam paths and said common axis, said electron gun means including cathode means and a lrst and a second electrode spaced along said axis between said cathode means and said target for providing a plurality of converging lenses one in the path of each beam, a third electrode spaced along said axis between said second electrode and said target for forming a plurality of principal focusing lenses one in the path of each of said beams, said rst electrode including a plurality of tubular members and an apertured plate, said plate having an aperture in the path of each of said beams, said tubular members mounted on said plate with one tubular member over each aperture and an open end of each of said tubular members adjacent said second electrode, said target electrode including a support plate having a plurality of groups of phosphor dots with one phosphor dot of each group having a different color of luminescence when bombarded with electrons, and a masking electrode closely spaced from said support plate between said support plate and said electron gun means for masking all except one of the phosphor dots of each group from the electron beam of each gun.

11. A cathode ray tube comprising, electron gun means for providing a plurality of electron beams along respective paths spaced from a common axis, a target electrode spaced from said electron gun means and mounted transversely to said beam paths and said common axis, said electron gun means including cathode means and a rst and a second electrode spacedalong said axis between said cathode means and said target for providing a plurality of converging lenses one in the path of each beam, a third electrode spaced along said axis between said second electrode and said target for forming a plurality of principal focusing lenses one in the path of each of said beams, said first electrode including a plurality of tubular members and a plate having an aperture therethrough aligned with each beam path, and means mounting one of said tubular members coaxially on each beam path with one end enclosing an aperture through said plate and with the other end of each of said tubular members adjacent said second electrode, said target electrode including a support plate having a plurality of groups of phosphor dots with one phosphor dot of each group having a dilferent color of luminescence when bombarded with electrons, and a masking electrode closely spaced from said support plate between said support plate and said electron gun means for masking all except one of the phosphor dots of each of said groups from the electron beam of each gun.

References Cited in the file of this patent UNITED STATES PATENTS 2,170,944 Glass et al Aug. 29, 1939 2,227,484 Bouwers Jan. 7, 1941 2,345,282 Morton et al Mar. 28, 1944 2,381,320 Tawney Aug. 7, 1945 2,563,500 Snyder, Jr. Aug. 7, 1951 2,587,074 Sziklai Feb. 26, 1952 2,660,612 Wood, Jr Nov. 24, 1953 2,661,436 Van Ormer Dec. 1, 1953 2,690,517 Nicoll et al Sept. 28, 1954 

